<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  <script>
    var str = 'how are you ?';
    console.log(str.slice(1,9))//slice(开始位置，结束位置[不包括])
    console.log(str.substr(1,3))//substr(开始位置，截取几个字符)
    console.log(str.substring(1,9))//substring(开始位置，结束位置[不包括])
  </script>
</body>
</html>